DE29623287U1 - Prism for a data cartridge - Google Patents

Description

Prisma for a data cartridge

The invention relates to reflection mechanisms for deflecting light through a tape arranged in a data cartridge.

5 Tape placed in a data cartridge is often provided with holes that serve as codes for the drive in which the data cartridge is to be used. The holes can indicate, for example, that the drive has reached the end or beginning of the tape, or that the end

10 or the beginning of the tape is near, or they can identify the exact type and length of tape in the cartridge inserted into the drive. The tape itself is usually opaque, and the drives are usually equipped with a light source and a light

15 detector to detect the presence or absence of such holes. Normally the light is positioned above or below the cartridge and the detector is located on the front of the

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Cartridge. The light shines through the top of the cover (which is typically transparent) or through a window cut into the metal base plate of the data cartridge. The light is then reflected by a mirror in such a way that it is bent at approximately 90° toward the tape. If a hole is formed in the tape, the light passes through the hole and exits the front of the transparent cover where it is detected by a photocell located in the drive. Also, sometimes the tape has multiple holes formed across its width, and a drive must be able to make an accurate determination of the number of holes based on the amount or position of light passing through the holes.

In some applications, the mirror is replaced by a prism. For example, EP 0 499 400 A1 describes a structure in which a prism is used instead of a mirror and lists several advantages of using a prism over a mirror.

In some applications, the use of a prism can cause problems. In certain cartridges, the light is usually directed upwards through the bottom of the cartridge, then angled towards the tape (by the prism or a mirror) and detected at the front of the cartridge after passing through a hole formed in the tape.

However, in drives from at least one manufacturer, the light is always directed backwards, i.e. it first shines through the holes formed in the tape, is then reflected to the bottom of the cartridge 5 and then detected at the bottom of the cartridge. Furthermore, in the drive of this

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The manufacturer places the light source and detector off-center relative to the prism in the direction of tape movement. This seems to make little difference if a mirror is used in the cartridge to angularly deflect the light. However, it has been found that using a prism can cause disturbing phantom pulses. This is particularly problematic when it is necessary to determine precisely whether there is a single hole or several holes in the tape.

A prism also causes problems because it requires a fairly large mass of material. In particular, the main body of the prism must be filled with material. This has several disadvantages:

First, the sheer presence of the amount of material increases costs. In addition, the material requires a longer period of time to harden, causing a long cycle time in a mold.

Second, most such prisms ¹ are manufactured by molding. Many types of thermoplastic materials experience shrinkage during curing. Large masses of plastic tend to develop sink marks. Depending on the location of the sink mark, this can affect or even eliminate the desired optical properties of the prism.

These problems, which arise from the mass of the prism body, are avoided by using a mirror, e.g. according to the teaching of published Japanese Patent Application Nos. 5-225,750, 5-225,751 and 5-225,752. However, mirrors also cause typical problems. It is difficult to make a mirror of such a size.

to be mirrored on the side closest to the tape. Thus, the primary reflection is usually from the side of the mirror facing away from the tape. This means that the light must pass through the front of the mirror before hitting the primary reflection surface and then return on its way through the front surface of the mirror. Furthermore, the disadvantage is that the front surface of the mirror is usually angled so that it produces a secondary reflection. This results in the same phantom pulse problem that occurs with some of the prisms described above.

The invention is based on the discovery that the reason a prism does not work well when the drive outputs light rearward (i.e., through the holes in the tape) through the prism, or when the light and/or detector are located off-center from the prism, is because there is too much stray reflection in the prism. When the light is sent through the prism in the usual direction (rearward through the tape), the internal reflection occurring in the prism is usually not important if the sensors are correctly aligned - the sensors in the drive are located fairly close to the holes in the tape, and any light passing through a hole will be in the correct alignment to indicate that a hole is present. However, when light passes through to the rear, each hole acts as a 0 small light source, and the light emerging from it can reflect both from the angled face of the 5 prism (as intended) and from the sides of the prism (which is not normally intended). This 5 multiple reflection can be interpreted by the drive sensor as the presence of multiple holes and make it difficult to determine the actual number of holes that

present at that point on the tape. This problem is exacerbated when there are actually multiple holes. Similar problems can also occur when the light passes through in the usual direction, namely when the light source and/or detector are located off-center (and thus closer to the sides of the prism).

This is a rather surprising finding considering the relative duration of the light pulse and the typical sensor clock pulse rate in such systems. The difference between the path lengths of the light taking the slightly longer path to the sensor and the light not reflected from the end faces is in the order of only a few millimeters, so the time delay for the light in this second pulse is in the order of 10" ^L1 seconds. The relevant clock cycle time for the computers detecting these pulses is in the order of 10' ⁸ or 10" ⁹ 0 seconds.

The invention addresses this problem by several possible means. First, the sides of the prism are frosted, coated, ribbed, textured or otherwise made substantially diffusing or non-reflective to minimize stray reflections. Alternatively, the sides are angled such that most of the reflections from them are directed substantially away from the detector or into a frosted portion of the prism or at least minimally overlap the position of the detector.

This principle can also be used for non-triangular prisms, e.g. those described in EP 0 499 400 Al, by making the parts of the prism that do not emit light

are intended to reflect, are frosted and/or angled so that reflected scattered light is diffused, absorbed or deflected.

According to another aspect of the invention, the problem is solved by providing multiple mini-prisms instead of a single large prism. In particular, the main body of the prism is left hollow rather than filled with material. The side of this void closest to the belt is simply a vertical wall. Thus, light passes in the perpendicular direction through this wall, minimizing reflection from the wall. The side opposite this wall, which would be an angled surface in a mirror, is instead a stepped surface. Thus, light passes in the perpendicular direction through the stepped surface, again minimizing reflection. The light is then reflected from the angled primary reflection surface of the prism and then exits through the other side of the step (or the next step) perpendicular to the step surface.

In this design, the only angled surface that the light typically hits is the intended primary reflection surface. All other interactions are perpendicular to the surface, so no significant unwanted reflection occurs.

Preferably, the prism main body is closed by sides 0. Furthermore, one or both of these sides may be provided with stepped shoulders, but having angled surfaces instead of vertical surfaces.

In this way, light enters the step through a surface that runs almost vertically, but is then reflected within the stepped shoulder

reflected without having the possibility to exit again.

Preferably, the outside of one or both of the prism sides has similar angular steps.

Preferably, all areas of the prism from which no reflection is to occur can also be frosted.

Finally, the reflecting surface of the prism preferably has a slight concave curvature. This curvature helps to focus the incoming light towards the detector if any refraction occurs.

In the following, the invention is described in more detail in connection with the figures listed below.

Fig. 1 shows an oblique perspective view from above of a data cartridge designed according to the invention.

Fig. 2 shows a partially sectioned view along the line 2-2 in Fig. 1.

Fig. 3 shows a partial bottom view of the data cartridge according to Fig. 1, showing the window formed in the base plate.
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Fig. 4 shows a bottom view of the prism of the data cartridge according to Fig. 1.

Fig. 5 shows a top view of the prism according to Fig. 4.

Fig. 6 shows a cross-sectional view similar to Fig. 2 of a second embodiment of a data cartridge designed according to the invention.

According to Fig. 1, a data cartridge 10 comprises a base plate 12 and a cover 14 with top, front, left, right and rear sides 15-19. The base plate 12 and the cover 14, when assembled, form a data cartridge housing. The housing contains the various components of the data cartridge, e.g. a tape 22 (visible in Fig. 2). Sometimes holes 24 are formed in the tape 22 at various positions, which a drive in which the data cartridge 10 is used must be able to detect.

A combined prism and window part 30 is provided in the data cartridge. The prism 30 is made of a transparent material, usually plastic, and generally comprises three parts: a main prism body 32, a bridge part 34 and a window part 36, as shown most clearly in Fig. 2. Although the main body 32 is shown as a conventional triangular prism, alternative prism structures may also be used, e.g. the curved prism structure shown in published EP 0 499 400 A1.

Both surfaces 35,37 of the window part 36 are surfaces with optical quality, and preferably the window part 36 closes an opening 39 formed in the cover 14.

The prism main body 32 has a front portion 40 and a rear portion 42. It also has sides 46 (shown most clearly in Figs. 4 and 5).

The front portion 40 has a front or outer surface 48 and a rear or inner surface 50 which are generally substantially parallel to the belt 22 and substantially perpendicular to the base plate 12 and are optical surfaces.

The rear portion 42 has an angled rear or outer surface 52 which may be mirrored if desired. The rear surface 52 is disposed at an angle greater than the critical angle of reflection relative to the central axis of the incident region of the light path A. Preferably, the rear surface 52 is at an angle of approximately 45°. A series of steps 54,56,58,60 are formed on the front or inner surface of the rear portion 42. Each step 54,56,58,60 has a first flat surface 54a,58a which is substantially perpendicular to the centerline of the horizontal region of the light path A, i.e. substantially parallel to the belt 22 0 and perpendicular to the base plate 12. Each step further has a second flat surface 54b,58b which is substantially perpendicular to the centerline of the vertical portion of the light path A, i.e. substantially parallel to the base plate 12. The corners 54c,58c should be as sharp as is reasonably practicable given the molding techniques involved, e.g., with a radius of about 0.001 inch (25 μm) or less. (The steps 56,60 have analogous surfaces and sides, but for clarity of the drawings, the reference numerals have been omitted.) The surface 62 should be substantially perpendicular to the vertical portion of the light path A, i.e. substantially parallel to the base plate 12. The surface 64 should be substantially perpendicular to the horizontal portion of the light path A, i.e. substantially parallel to the band 22 and perpendicular to the base plate 12.

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Together, the surfaces 54,56,58,60,62,64 and the sides 46 form a cavity 66 in the prism main body 32. Preferably, the corner 62a is slightly rounded, e.g., by about 0.010 inch (250 /im) to minimize the risk of the surface 50 being damaged by the mold. All surfaces 52,54,56,58,60,62,64 should be of optical quality.

Although the front surface of the rear portion 42 is described and shown as having four steps, it will be apparent to those skilled in the art that a greater or lesser number of steps may be used.

Typically the maximum number of steps is limited by the manufacturing technique used, e.g. in injection molding the smallest single step that can be easily manufactured has areas of about 0.001 inch (25 μm). The physical limitation on the number of steps would normally be much lower, about 10 times the wavelength of the light used. Below this range the light would be likely to be affected by significant refraction effects.

The rearmost part 70 of the rear section 42 extends rearward in a substantially flat direction, i.e. the rear surface 72 along the part 70 is no longer angled. Furthermore, the bottom of the part 70 is provided with a flange 74 and/or a base part 78. The flange 74 and/or the sides 79 of the base part 78 and the front surface 48 are precisely positioned relative to the rear surface 52 so that when positioned in the opening 76 formed in the base plate 12, the entire prism structure 30 is precisely positioned relative to the opening 76. According to the usual specifications for a normal drive, the base plate 12 is used to support the cartridge IO as a

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to position the whole exactly relative to the drive so that when the cartridge 10 is inserted into the drive, the exact positioning of the prism structure 30 relative to the opening 76 of the base plate 12 thereby positions the cartridge 10 exactly relative to the drive.

In operation, the incident light typically travels upward along path A, passes through one of the horizontal surfaces of the steps 54, 56, 58, 60, is reflected from the angled surface 52, passes through one of the vertical surfaces of the steps 54, 56, 58, 60, and passes through the rear surface 50, the front surface 48, a hole 24 formed in the band 22, and the window 36. As can be seen, the path of the light ensures that any interaction with surfaces other than surface 52 is in the vertical direction, thus minimizing stray reflections. As can also be seen, the light travels through the system in the opposite direction, with the same minimization of stray reflections.

Although the steps 54,56,58,60 are shown in cross-section as being substantially rectangular, they need not be rectangular if the light path is not rectangular. The essential aspect for each surface is that the steps are substantially perpendicular to the light path entering and leaving the surface.

It may happen that light undesirably passes through the region 80 below the lower edge of the band 22. To minimize any resulting interference, the lower parts of the surfaces 35,37 of the window 36 and/or the surfaces 48,50 of the front section 40 may be frosted, notched,

ribbed or otherwise designed to diffuse light. As is known, the "frosted" surfaces can be achieved simply by roughening the corresponding surface of the mold in which the prism is cast. In addition, the horizontal design of the rear surface 52 at the rear part 70, shown at 72, stops downward reflection of light at this lower part of the prism. Instead, the light passes through the lower region of the vertical wall 60a or the vertical wall 64 and simply passes through the rear part 70 without being reflected downward.

As can be seen, the design described here provides good reflection of the light beam in the desired directions while minimizing the mass of material required in the prism main body 32. Traces of sink marks are essentially eliminated since the total amount of plastic required is considerably less. Cycle time can be significantly reduced since only thin pieces of plastic are required.

Unfortunately, the cavity 66 can cause some problems of its own. In particular, the inner surfaces of the walls 46 are much closer to the light path A than the outer surfaces of the walls 46. In a solid prism, only the outer surfaces would tend to reflect stray light. However, if an inner surface is present, the inner surface can also reflect stray light. Frosting may eliminate this problem. However, there is also the possibility that it will not.

Therefore, according to a further aspect of the invention, additional prism structures are provided to

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reflection. These structures are most clearly shown in Figs. 4 and 5. In Fig. 4, angled steps 80,82,84,86 are provided on the inner surface of the side 46. The steps 80,82,84,86 may be provided on one or both of the walls 46, depending on the expected positions of the light source. For example, if the light source is expected to be offset to one side of the prism but not to the other side, steps 80,82,84,86 on a single side 46 may be sufficient. Each of the angled steps 80,82,84,86 is preferably formed at an angle such that its surface 80a,82a,84a,86a closest to the tape is substantially perpendicular relative to the light entering from the tape hole 24. The angled surface 80b,82b,84b,86b of each step is substantially parallel to the light entering from the band hole 24. In this way, the light can easily enter the angled step 80,82,84,86 but is held therein without having any opportunity to escape. Preferably, the sides 80b,82b,84b,86b are frosted to assist this effect.

Preferably, as shown in Fig. 5, similar steps 90,92 are formed on the outer side of the side 46. In this case, the sides of the steps 90,92 are such that the short surfaces 90a,92a are substantially perpendicular to the direction of the light so that the light passes through them, and the longer sides 90b,92b are substantially parallel to the light so as to prevent the light from passing through them. As in the case of the inner angled steps 80,82,84,86, the outer steps 90,92 can be formed on one or both of the sides 46. Furthermore, as shown in the drawings, the number of inner and outer steps need not be limited.

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to be equal. Preferably, the angled sides 90b,92b are frosted.

As will be apparent to those skilled in the art, the use, number, size and exact angles of the various inner and outer steps 80,82,84,86,90,92 can be varied depending on the exact design of the prism to be used. It will also be understood that the surfaces of the outer angled steps 90,92 and any other surfaces of the prism that are not intended to transmit light can be frosted, ribbed or otherwise made opaque.

Preferably, the surface 52 is slightly curved, as shown in greatly exaggerated form in Fig. 2 by the dashed line 52'. This slight curvature helps to refocus the light beam as it travels to the photodetector. Ideally, the portion of the curve 52' tangent to the surface 52 is aligned with the hole 24 to optimize this effect.

Finally, as shown most clearly in Figs. 4 and 5, flanges 96 may be provided on each side of the sides 46 in which pin holes 98 are formed. These pin holes 98 may be used in conjunction with suitable pins 100 (see Fig. 2) in the cartridge 100 to assist in positioning the prism in the cartridge. Preferably, the bridge portion 34 is somewhat flexible and the spacing of the pins 100 relative to the front face 16 of the cover 14 is such that the window portion 36 is in effect spring biased rearward against the cover 14. Additionally (or alternatively), the spacing of the flange 74 and/or the base portion 78 may be such as to assist in this bending effect. Preferably, the lower edge

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of the window part 36 is slightly curved towards the prism main body 32 so that this part, when inserted into the cover 14, is in effect spring-loaded into a state of slight tension (with its surfaces aligned with the front face 16).

Fig. 6 shows a view similar to Fig. 2 of an alternative embodiment of a reflection device according to the invention, in which the step concept with a mirror instead of a prism is used. In this embodiment, a cartridge 110 has a transparent cover 112 and a base plate 114 and a window 116 formed in the base plate 114. The reflection device is a mirror 118 with a first section 120 and a second section 122. The first section 120 can be mounted on the base plate 114, in the window 116 or above the window 116. Preferably, the first section closes the window 116. The second section 122 has an outer surface 124 which is arranged at an angle which is - preferably 45° - greater than the critical angle of the incident light path B and can be mirrored if desired. The inner surface of the mirror 120 is formed by a plurality of steps 126, in much the same way as the inner steps 54, 56, 58, 60 of the prism 32 according to the first embodiment. The surfaces of the window 116, the steps 126 and the outer surface 124 are optical surfaces.

0 The light passes through the first section 12 0 and through one side of a step 126, is reflected from the outer surface 124, exits through another side of a step 126, passes through a hole 130 formed in the band 128 and exits through the front 13 2 of the 5 transparent cover 112. All interaction with surfaces other than the outer surface 124 is essentially

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perpendicular to the surface so that unwanted reflections are minimized.

As will be apparent to those skilled in the art, in much the same way as in the first embodiment, the lower portions of the front surface 132 of the cover 112 may be frosted to prevent light from passing under the band 128, and the shape of the rear end 134 of the mirror may be adapted to minimize reflection from this source. Furthermore, the outer surface 124 may be made slightly concave, as is the case with surface 52'.

Of course, these embodiments described as examples are not to be construed as limiting the scope of the invention in any way. In view of the foregoing description, further modifications of the invention will be apparent to those skilled in the art. For example, although the invention has been described in connection with triangular prisms and mirrors, it can also be applied to non-triangular prisms and mirrors. The descriptions are merely intended to set forth particular embodiments from which the invention can be clearly understood. Thus, the invention is not limited to the embodiments described or to the use of particular elements, dimensions, materials or configurations mentioned herein. The invention includes all alternative modifications and variations that fall within the principles and scope of the appended claims.

Claims (11)

EXPECTATIONS 1. Reflection device for a data cartridge (10) for use in a drive with a main optical axis (A) for incident light, the device having a transparent main body (32), characterized in that the main body has: a) a first portion (40,120) having an outer surface (48), an inner surface (50) substantially parallel to the outer surface (48) and at least one first end, both the inner and outer surfaces being substantially perpendicular to the light path axis (A,B) when the reflection device is in a drive, b) a second section (42,118) having an outer surface (52,124), an inner surface (54,56,58,60, 126) and at least a first end, the first end of the first section (40,120) being adjacent to the first end of the second section (42; 118) and, when the reflecting device is in a drive, the outer surface (52,124) of the second section (42,118) being at an angle relative to the light path axis (A,B) that is greater than the critical angle; and c) a plurality of steps (54, 56, 58, 60, 126) formed on the inner surface of the second section (42, 118), each having a first surface (54a, 58a) which is substantially perpendicular to the main optical axis (A, B) for the incident light when the reflecting device is in a drive, and an adjacent second surface (54, b/58b) which is substantially parallel to the main optical axis (A, B) for the incident light, - 18 - if the reflection device is located in a drive. 2. Device according to claim 1, characterized in that the main body (32) comprises: a) a bridge portion (34) projecting outwardly from the main body (32) adjacent the first ends of the first and second sections (40,42); and b) a transparent window part (36) which is arranged at a distance from the main body (32) and projects downwards from the bridge part (34) substantially parallel to the surfaces (48, 50) of the first part (40). 3. Device according to claim 1 or 2, further characterized in that the first section (40) and the second section (42) each have two lateral edges, and in that the main body (32) has two sides (46) which each extend between the lateral edges of the first and second sections (40, 42) and connect the edges to one another. 4. Device according to claim 3, further characterized in that the first and second sections (40,42) and the sides (46) define a cavity (66) between them. 5. Device according to claim 3, further characterized in that each side (46) has an inner surface and an outer surface and at least one surface of at least one side has a plurality of steps (80, 82, 84, 86, 90, 92) formed thereon, each of which has a first surface (80a, 82a, 84a, 86a, 90a, 92a) which, when the reflection device is located in a drive, runs substantially perpendicular to a light path that propagates along the main optical axis (A, B) for the incident light to the stage, and have an adjacent second surface (80b, 82b, 84b, 86b, 90b, 92b) which, when the reflection device is located in a drive, runs substantially parallel to the light path that propagates along the main optical axis (A, B) for the incident light to the stage. 6. Device according to claim 5, further characterized in that a plurality of such steps (80,82,84,86,90,92) are formed on both the inner and outer surfaces of at least one of the sides (46). 7. The device of claim 1, further characterized in that the first portion (40) has a second end opposite the first end, and a portion of at least one of the inner and outer surfaces of the first portion (40) and the first end of the outer surface of the second portion (42) proximate the second end is frosted, coated or otherwise treated to be diffuse. 8. Device according to one of claims 1 to 7, further characterized in that the outer surface (52,124) of the second section (42,118) is at substantially 45° to the light path axis (A, B) when the reflection device is located in a drive. 9. Device according to one of claims 1 to 8, further characterized in that the outer surface (52,124) of the second portion (42,118) is slightly concave. ■» « - 20 - 10. Device according to one of claims 1 to 8, further characterized in that the device is arranged in a data cartridge (10) which has a base plate (12) with a window (76) formed therein, and the first and second sections (40, 42) and the sides (46) abut against the base plate window (76) and substantially close it. 11. Device according to claim 10, further characterized in that the device has a base part (79) which extends downwards into the base plate window (76) in order to position the device precisely in relation to the base plate (12).